Metal phosphide filler for grinding wheels



United States Patent once 3,032,404 Patented May 1, 1962 3,032,404 METALPHOSPHIDE FILLER FOR GRINDING WHEELS Thomas E. Douglass, Dayton, andClarence B. Tilton, Springfield, Ohio, assignors to Simonds Worden WhiteCompany, Dayton, Ohio, a corporation of Ohio N Drawing. Filed Apr. 17,1961, Ser. No. 103,247 7 Claims. (Cl. 51-298) This application is acontinuation-in-part of an earlier application Serial No. 840,819, filedSeptember 18, 1959, now abandoned in favor of the present application.

This invention relates to abrasive articles such as grinding wheels andmore particularlyv to grinding wheels in which abrasive grains areunited into an integral unit by bonding agents containing an'improvedfiller material.

One object of the present invention is to provide an improved grindingWheel of the types intended for snagging, semi-finish grinding andfinish grinding, yield-ing higher ratios of material removed from theground article per unit of weight loss of the grinding wheel than haveheretofore been considered possible. Another object of the invention isto provide a grinding wheel comprising abrasive grains, held together bya filler containing bond in Which the filler consists of one or morecompounds of phosphorus in which the phosphorus is di-, triorpenta-valent.

A more specific object of the invention is an improved grinding wheel inwhich heavy metal phosphides are employed as fillers.

Still a further and preferred object is an improved grind-ing wheel inwhich the filler includes a heavy metal phosphide and potassium aluminumfluoride.

More specifically, it is an object of invention to provide an abrasivegrinding wheel wherein metal phosphides and especially heavy metalphosphides either alone or accompanied by potassium aluminum fluorideconstitute the fillers, and wherein, together, with resinoid, vitrifiedor rubberoid bonding agents, the fillers and the grains of abrasivematerial are united into a unitary or integral body of the wheel of theresinoid, vitrified or rubber bonded type.

These and other objects will become apparent in the description whichfollows.

One manner in which the quality of a grinding wheel has been expressedis set forth in the ratio of total pounds of material removed from thesurface being ground by the grinding wheel in one hour compared with thetotal pounds of the wheel which are lost or consumed per hour duringsuch use. The determination of the actual efficiency of a grinding wheelis further complicated by the effects of pressure, temperature andpossible chemical action at the high pressure and high temperatureexperienced by the Wheel in actual service.

One of the more generally accepted theories of grinding action at thepoint of contact between the grinding Wheel and the surface being groundis that when an abrasive grain removes a fragment of metal, this fragment should be reacted chemically or altered in 'some way so that itwill not weld back to the metal surface from which it has been cut ortorn. Since the temperature at the point of grinding is often in theregion of 2000' F. to 2200 F. it will be readily appreciated that mostof 'the materials that have previously been used as fillers in grindingwheels will become chemically active and may even be decomposed inservice.

The present invention pertains to improvements in grinding or abrasivewheels of the type described in Kistler United States Patent 2,308,981and others of a similar nature, intended specifically for snagging,semi-finish grinding or finish grinding, whether of the resinoid,vitrified or rubber-bonded type. Such wheels are generally composed ofabrasive grains such as aluminum oxide or silicon carbide or otherabrasive particles which may constitute from about 60% to as much as byweight of the total wheel by weight. The abrasive particles are heldtogether by the bonding agents used-whether resin, rubber or otherbonding material. In addition, the bond often contains interpersedthroughout the composition one or more materials designated as fillers.

Upon studying the performance of a large number of fillers previouslyknown in the art including sulfides, cryolite, fluoborates, varioussalts including salts of lead, and other materials not hitherto known tobe useful, and after comparison of the quality or performance ratings ofgrinding wheels formulated with such materials, it was found that wheelscontaining heavy metal phosphides gave outstanding service and thattheir performance was enhanced still further when a small butsignificant amount of potassium aluminum fluoride was incorporated inbond composition.

While we do not wish to be bound by any specific theory, it appears thatheavy metal phosphides and particularly manganese phosphides areeffective largely because of superior chemical properties at the hightemperatures encountered in service. The potassium aluminum fluoridewhen present appears to melt at these temperatures and to act as alubricant for the metal fragments detached from the surface being groundand thereby prevents them from welding onto the freshly ground surface.

The heavy metal phosphides and other materials employed as fillers arepreferably dry, finely divided solids in order that they may be readilyinterspersed throughout the bond. As a general rule, the larger theamount of filler the higher is the quality of the wheel, up to a point;after that, greater amounts detract from the quality of the wheel. Theimproved filler of the present invention should constitute from 10% to40% by volume of the total bond and preferably between 20% and 40% forcertain types of grind-ing wheels.

One example of the manufacture of a grinding wheel according to thisinvention is as follows:

A suitable quantity of abrasive grains, e.g. alumina or silicon carbide,is Wet with furfural in a mixing chamber. In a separate mixing tubsuitable quantities of A stage phenolformaldehyde resin, manganesephosphide, lime (CaO), potassium aluminum fluoride and hexamethylenetetramine are blended to a homogeneous dry powder mass. This dry mixtureis added slowly to the furfural wetted abrasive grains with mixing,until a uniform granular mix is obtained. The mixture is put into amold, pressed and cured at approximately 350 F. in the mold.

Quantities of the various ingredients vary widely for differentstructures and grades of wheels, as is known in the art.

One typical formulation used with excellent results is In thiscomposition the phosphide comprises about 5.29/ 15.37 or 35% of thefiller, by volume and the filler comprises about 36% of the bond, byvolume.

In a comparative test involving grinding carbon steel (SAE 4145) twogrinding wheels prepared as above described and containing identicalgrade structure and resinoid bond composition except that one fillercontained 35.5% by volume of maganese phosphide and the other fillercontainer 35.5% by volume of FeS. The ratio of M/ L, i.e. pounds ofmetal removed/ unit of wheel lost in grinding with the wheel bearing thephosphide was 61.867 where the same ratio for the sulfide bearing wheelwas only 45.93; an improvement of 32.5% in performance.

The improvement in performance is further indicated by the factor knownas cutting efliciency, or the ratio of the energy input in kwh. to thepounds of metal removed. In the same test these ratios were as follows:0.160 for the phosphide bearing Wheel and 0.175 for the sulphide bearingwheel. Since grain grade and structure were the same, the wheel with thelower cutting efiiciency is the most economical. It can be readily seenthat the formula for cutting efficiency,

E kwh. (energy input) M(lbs. metal removed) Phosphide Sulfide Percentbearing hearing improvewheel wheel ment Nil L 60. 48 45. 93 32 Anothermethod of determining the performance of the grinding is by measuringthe number of pounds of metal a grinding wheel can remove per hour.Tests were conducted under identical conditions with wheels prepared asabove described and the following results were obtained:

Sulfide Phosphide Phosphide Metal removed/hour 46. 35 50. 18 49. 77

Instead of manganese phosphide, we have found that other heavy metalphosphides may be used with like results, including the phosphides ofchromium, molybdenum, iron, copper, nickel, cobalt, tin, aluminum,vanadium and other heavy metals, in which the phosphorus exists in itsdivalent, trivalent or pentavalent form.

In terms of the total bond, it is preferred that the phosphideconstitute between about and 50% by weight of the total bond weight andthat, when present, the potassium aluminum fluoride should constitutefrom -25% of the total bond by weight. Optimum results on snaggingwheels were obtained with wheels in which the phosphide constitutedabout 36.1% by weight of the total bond. With an abrasive wheel of thiscomposition, a ratio of weight of material removed to weight of material10st from the wheel as high as 61.8:1 have been obtained.

The invention may be embodied in a rubber bonded grinding wheel whichmay be formed by blending on suitable mills, either natural or syntheticrubbers, manganese sulfide, suitable rubber curing agents, e.g. sulfur,accelerator, ZnO and anti-oxidants together with the abrasive gram.

Any of the manganese phosphides may be utilized as an active filler inaccordance with this invention either alone or in combination with othermetallic or non-metallic phosphides or with such other agents ascryolite, potassium aluminum fluoride or other fillers that may besuitable for this purpose. That is to say that these phosphides may beused in combination with other known active agents to decrease the costof grinding by the user. The composition and structure of the abrasivearticle may be varied widely and the manganese phosphide may beincorporated into a grinding wheel in any suitable or desirable manner.

The above disclosure is to be interpreted as illustrating the generalprinciples of this invention and the preferred types and compositions ofabrasive articles, and not as limitations on the invention, except as itmay be limited by the appended claims.

What is claimed as new is as follows:

1. An abrasive article comprising abrasive grains, a bond materialuniting the grains as an integral body and a filler consistingessentially of finely divided solid heavy metal phosphide interspersedthroughout the bond.

2. An abrasive article comprisingabrasive grains and a resinoid bondwhich units the grains as an integral body, said bond having intimatelyassociated therewith a filler consisting essentially of a heavy metalphosphide which constitutes from 10 to 40% by volume of the bond mass.

3. An abrasive article comprising abrasive grains, a vulcanized rubberbond uniting the grains integrally and a filler consisting essentiallyof from 10 to 40% by volume of heavy metal phosphide interspersedtherethrough.

4. An abrasive article comprising abrasive grains, a bond uniting thegrains as an integral body which has as its primary constituent aphenol-formaldehyde condensation product, and a solid granular fillerincorporated in the bond consisting essentially of heavy metal phosphidein an amount which constitutes from 10 to 40% of the bond mass, byvolume.

5. A grinding wheel comprising abrasive grains, a bond uniting thegrains as an integral body which has as its primary constituents aphenol-formaldehyde condensation product, and manganese phosphidedispersed through the bond as a filler constituting from 10 to 40% ofthe volume of said bond.

6. An abrasive airticle comprising abrasive grains, an organic bonduniting the grains as an integral body and a filler interspersedthroughout the bond consisting essentially of potassium aluminumfluoride and heavy metal phosphide which together constitute from 10 to40% by volume of the bond mass.

7. An abrasive article comprising abrasive grains, an organic bonduniting the grains as an integral bodyand a filler interspersedthroughout the bond consisting essentially of potassium aluminumfluoride and manganese phosphide which together constitute from 10 to40% by volume of the bond mass.

References Cited in the file of this patent UNITED STATES PATENTS2,216,135 Rainier Oct. 1, 1940 2,308,981 Kistler Jan. 19, 1943 2,308,982Kistler Jan. 19, 1943 2,939,777 Gregor et al June 7, 1960 2,940,841Gregor et a1 June 14, 1960 2,940,842 Phillips June 14, 1960

2. AN ABRASIVE ARTICLE COMPRISING ABRASIVE GRAINS AND A RESINOID BONDWHICH UNITS THE GRAINS AS AN INTEGRAL BODY, SAID BOND HAVING INTIMATELYASSOCIATED THEREWITH A FILLER CONSISTING ESSENTIALLY OF A HEAVY METALPHOSPHIDE WHICH CONSTITUTES FROM 10 TO 40% BY VOLUME OF THE BOND MASS.